Gentlemen (and ladies too),
CAR: 1994 Olds 88, 3800 V6, auto
PCM: 16183247 BHDU
PROBLEM: intermittent MIL lamp, EGR pintle position error.
ANALYSIS (so far): using laptop PC with PCM scan and control software, retrieve
historical data. EGR problem observed. Clear PCM codes. Perform PCM relearn
procedure. Scan active data during three seperate 15 minute road tests. Observe
EGR problem has reoccured, and that no other codes were set.
Chart (plot) the three EGR related values from PCM against time:
ADEGRPOS- EGR actuator voltage
DSEGRPOS- desired EGR actuator position
EGRPOS- EGR actuator position
The chart shows that the current EGR pintle position is way out of wack from
the desired position. The following table is an excerpt from the data stream
showing the EGR data activity. Example: in time frame 945, the EGR control
voltage was 2.22v, the current EGR position is at 24.3% open, and the PCM
desired position is 23.5%. If I am correct, then the PCM is pulling B+ voltage
(that originates from the 15amp cruise control fuse in the relay center) down
to 2.22v at pin RA16, and 2.22/4.65=.477 or 47.7%. But the desired EGR position
is 23.5%! In frame 946, you can see that the EGR position then moved to 40.4%.
FRAME EGR volts EGR %POS Desired EGR %POS
945 2.22 24.3 23.5
946 1.82 40.4 21.2
947 1.08 12.5 30.2
948 1.06 4.31 37.3
949 2.27 47.8 38
950 2.18 48.2 38
951 1.71 43.9 39.6
952 1.69 27.8 39.2
(NOTE: the min and max EGR control voltage observed during the run was .53v and
ACTIONS TAKEN: continuity test all wires from PCM to EGR, ok. Check PCM harness
female pins for good contact with PCM backplane male pins, all good and tight.
Swap EGR valve with known good unit, repeat ANALYSIS, same results.
QUESTION #1: what is the program logic in the PCM for controlling the EGR?
QUESTION #2: what kind of circuit is in the PCM that sends it output control
voltage to the EGR from pin RA16?
QUESTION #3: Is this a normal failure point in this model/year PCM?
QUESTION #4: anyone know where on the internet I can get the schematic for the
You can see the graphic plot here: http://www.glocktech.net/b
remove all "f"'s from address